US2530182A

US2530182A - Dual focus x-ray apparatus

Info

Publication number: US2530182A
Application number: US540384A
Authority: US
Inventors: Charles M Slack
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1944-06-15
Filing date: 1944-06-15
Publication date: 1950-11-14
Anticipated expiration: 1967-11-14
Also published as: FR948193A; GB593115A

Description

Nov. 14, 1950 c.. M. sLAcK 2,530,182

DUAL FOCUS X-RAY APPARATUS Filed June l5, 1944 IPM-gg .6. VaLr/vaf- INVENTOR imi' c. M. s4/Qca.

BY www ATTORNEY Patented Nov. 14, 195() DUAL FOCUSX-RAY APPARATUS Charles M..Slack, Glen Ridge, N. J., Vassigner -to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 15, 1944, Serial'No. 540,384

(Cl. Z50-98) 9 Claims.

VThe present invention relates to X-.ray apparatus .and moreparticularly to such apparatus employing a double-focusX-ray tube.

It is .now quite customary in the art to utilize an X-ray tube provided with two lamentary cathodes, one which produces a small focal spot by the passage of a relatively low current therethrough, thus adapting the tube for long exposures for purposes of uoroscopy, and a second higher current lamentary cathode which produces a larger focal spot for radiographic purposes. X-ray tubes of this type have proved quite satisfactory in saving the cost of an extra tube and wherein there is a sucient interim between the two types of diagnostic examinations.

"There are many instances, however, where the roentgenologist observes some phenomenon during `the course of a luoroscopic examination and wishes to immediately make a permanent record thereof by the making of a radiographic exposure.` This necessitates switching from the lowemission-small-focal-spot cathode to the highcurrent-large-focal-spot cathode. The disadvantage heretofore existent in such apparatus resides in the fact that it takes approximately a Vsecond or so for the high-current-large-focalspot-cathode to reach an electron emitting temperature before "the radiographic exposure can be made. Consequently this lapse of one second is a serious handicap in many instances because the particular organ previously observed during uoroscopy may change in position, shape or conditi-on, in performing'its natural function, so that a radiographtaken after the lapse of one second may not show the same condition intended to be radiographed.

- It is accordingly an object of the present invention to provide an X-ray apparatus employing a double-focus X-ray tube wherein the change from one focal spot to the other for the making of a radiographic exposure is accomplished without substantially any loss of time.

Another object of the present invention is the provision of an X-ray apparatus employing a double-focus X-ray tube wherein the high-cur- .rent-large-iocal-spot cathode is heated substantially instantaneously to an electron emitting temperature.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein: .Y Figure 1 is a schematic diagram of an X-ray apparatus constructed in accordance with the present invention, and Y Figure 2 is a schematic diagram of -a modication which `the X-ray apparatus `as shown in Fig. 1 may take.

Referring now -to the drawings in detail, an X-ray tube l5 is shown which is provided with an anode 6, a -low-current-small-focal-spot lamentary cathode l, and a high-current-large-focalspot lamentarycathcde- 8. The X-ray tube recei-ves electrical energy from a high potential transformer 9, having its primary winding IIl connected toa source of the Ycustomary 'commercial potential of `11B-23d volts through a suitable control'arra-ngement as noted by the legend. The secondary winding AI'2`is connectedthrough avbridge-arrangement of rectifying valve tubes I3 tothe anode 'E and a connection I l common to bcthrlamentary cathodes 'I and'S, inthe usual manner of full wave X-ray tube energizing circuits. 7 Y' rFor the purpose of heating the small vfocalspot iilamentary cathode I to an electron emitting temperature, it is connected to the ysecondary winding I5 of -a low tension 'heating vtrainsformer I6, and in a similar manner the larger focal-spot i'llamentary cathode 8 is connected to the secondary winding YVI -of another low tension heating Ytransformer I8. As shown, one end of the primary winding I9vof transformer I6 is connected to a conductor 2li extending through a switch 221to a suitable sou-roe of supply'designated LI, L2, such as the same ccmmercialsource adjustable impedance such 'as a resistance '29 and conductor SII-to the conductor'24 constituting the lother side of the supply source LI. Accordingly,

uponY closure ofswitch 22 both the primary windings IS and 28 are energized. However, the adjustable resistance '23 is so set that the secondary winding l5V delivers sufiicient energy to the small focal-spot-cathode 'I to heat it to an electron emitting temperature,` while the adjustable resistance 2-9 is set so that the secondary winding -I'I delivers just suiiicient Senergy to the largeA focal-spotcathode 8 as'to maintain it at a tem'- The 'remaining end of primary windperature where no electron emission occurs. Under these conditions, the X-ray tube is conditioned for fluoroscopy and the operator merely operates the customary controls which causes energization of the high voltage transformer 9 as desired.

When a radiographic exposure is desired, the diagnostician de-energizes the high voltage transformer 9 and moves a lm carrying cassette into the eld of X-radiations from the tube in place of the fluorescent screen or in supermDOSSd position with respect thereto. Movement of the cassette into a position for a radiographic eX- posure is normally utilized to close the requisite switches to change the apparatus from iiuoroscopic setting to a radiographic setting, or they may be manually operated, as desired. However, for the sake oi simplicity such switches are shown schematically in the present drawings.

Assuming now it is desired to make a radiographic exposure with the apparatus of the present invention and a cassette is moved into the field of radiations after de-energization of the X-ray tube. A switch 32 is then closed which completes a circuit from the conductor 2l (constituting one side of the supply source Ll) through a conductor 33, now momentarily closed pushed button switch 32, a normally closed switch 34 to the winding 35 of a relay 36, and thence to conductor 20 (constituting the other side of the supply source L2). The relay 36 is thus energized and raises its armature.

Movement of the armature of relay 36 interrupts the circuit to the primary winding i9 of low tension transformer i6 by opening its normally closed contact 26, thus de-energizing the small focal-spot cathode l. A second relay contact 3l closes which completes a self-holding circuit to relay winding 35 by short-circuiting the momentary contact button 32 through a conductor 36, and at the same time short-circuits the adjustable resistance 29, by means of a conductor 39, since the latter together with the conductor 38 constitute in eect an extension of the conductor 33, upon closure of relay contact 31.

Short-circuiting of the adjustable resistance 29 thus applies full line voltage to primary winding '28 of the low tension transformer i8 causing the secondary winding Il to deliver suiicient energy to the large focal-spot cathode to raise it to an electron emitting temperature. The apparatus thus far described diers very little from the prior art since it is known that by preheating the large focal-spot cathode to a temperature just below electron emission shortens the time required to raise it to an electron emitting temperature upon the further application of suilicient electrical energy thereto. Despite such preheating, however, a lapse of approximately one second occurs before the large focal spot cathode reaches an electron emitting temperature which all toc frequently means the loss of the particular phenomenon the diagncstician desired to radiograph.

To avoid such time lapse, the present invention raises the temperature oi the large focal spot cathode in the extremely short period of time of one-tenth of a second or less. For this purpose an energy storage device, such as a condenser 46, is provided, which is arranged to discharge its energy through the cathode, in substantially the same manner as shown and described in my application Serial No. 540,382, filed concurrently herewith, now Patent No. 2,420,844. As shown in the drawing, the condenser 4l) is charged to a desired potential from any suitable direct current source properly insulated from the high voltage, as indicated by the legend in the iigures. One such source may comprise a transformer and rectifying bridge arrangement, such as that shown for energizing the X-ray tube, but natura-lly of a much lower voltage than that of the high voltage transformer 9.

The discharge circuit for thev condenser 40 includes, in addition to the large focal-spotcathode 8, a three electrode control tube 42 having its cathode-anode circuit included in series with the condenser 46 and cathode 8. This tube 42 normally prevents discharge of the condenser 45 since its control electrode is supplied with a biasing potential from a source, such as a battery 43 and resistance 44, which is more negative than that supplied to the cathode of the tube 42. For controlling discharge oi condenser 4t by rendering the tube 42 conductive, its cathode and control electrode are connected to the secondary winding 45 of an insulation transformer 4E through a resistance 41.

The primary winding 48 of the insulation transformer 46 is included in the discharge circuit oi a further condenser 49, also charged from a suitable direct current source in the same manner as that for the condenser 4U, as previously mentioned. Discharge of this latter condenser 49 is also normally prevented by a three element control tube 5U similar to the tube 42. The control tube 56 likewise has a biasing potential applied to its control electrode from a suitable source, such as a battery 52 through resistances 53 and Sii, which is more negative than that applied to its cathode.

In order to render the tube 55 conductive, a further source such as a battery or the like 55 is provided which is connected to the cathode and control electrode by closure of a contact 56 of relay 36. Upon closure of this contact 56, the potential supplied to the control electrode of tube 5U is then made more positive than that supplied to the cathode by the battery 55, thus overcoming the bias supplied by the source, such as the battery 52, and immediately rendering tube 5G conductive. This causes condenser 49 to discharge through the primary Winding 48 of insulation transformer lit. The resulting energy impulse is induced in the secondary winding 45, which in turn is impressed across the cathodecontrol electrode of the trigger tube 42, which thus overcomes the negative bias impressed thereacross from the source 43 and making this tube conductive. This immediately causes the condenser 46 to discharge its stored energy through the large focal-spot cathode 8.

t is also to be noted that since the relay contact 56 closes its contacts simultaneously with the short-circuiting of the adjustable resistance 29 by closure of relay contact 37, the discharge of condenser 4B occurs simultaneously with the supply of increased energy from the secondary winding l1. Discharge of the condenser 4i] occurs in approximately 0.1 of a second (although this time can be shortenedby increasing the voltage or capacity of the condenser, as described in the above noted copending application), which thusraises the lamentary cathode 8 to an electron emitting temperature in the same period of time with the cathode then being maintained at such electron emitting temperature by the energy supplied from the secondary winding I'I. Y

.'pon .the cathode 8` thus reaching Aan electron emitting temperature, X-rays are generated for the time period for which the high tension transformer 9 is energized under the control of the usual timer and the desired exposure is made, The large focal-spot cathode 8 is accordingly raised to an electron emitting temperature very rapidly, i. e. in about 0.1,second or less, in lieu of the longer time of approximately one second as heretofore required. Since the time required for change-over f the apparatus from fluoroscopic to radiographic purposes is s0 greatly reduced, the phenomenon observed during a fluoroscopi'c examination can be readily radiographed before a change or alteration of such phenomenon occurs, as too frequently results in cases of human organs during their natural function, which cannot be accomplished with apparatus heretofore known t0 the art,

Having completed a radiographic exposure, the apparatus is again readily changed over for ucroscopic purposes by momentarily opening the switch 34, which, as above mentioned, may be operated by movement of the cassette out of the field of radiation from the X-ray tubeJ or by hand. Momentary opening of the switch 34 interrupts the self-holding circuit to the winding 35 of relay 36 causing its armature to gravitate and its normally open contacts 31 and 56 to again assume their open position and the normally closed contact 2 to again close. The closure of contact 26 accordingly completes the circuit to the primary winding I9, thus again energizing the small focal-spot cathode l and at the same time opening of contact 3l interrupts the short-circuit for the adjustable resistance .29, causing the latter to again limit the energy supplied by secondary winding Il to the large focal-spot cathode 8, whereby its temperature is maintained below electronemission.

In Fig. 2 a slight modication of the present invention is shown which diiers from that previously described in the manner of control. For example, in Fig. 2 the points A--B and X-Y correspond to the same points in Fig. 1 so that it will be seen that one end of each of the low voltage primary windings i9 and 28 are connected directly to the conductor 2l and constituting one side of the supply source Ll. conductor 2li in this modification connects to a double-throw switch or the like 6d, which in one position completes a circuit to primary winding i9 of low tension transformer I5, thus causing the secondary winding l5 to energize the small focal-spot cathode Similarly, movement ci the switch 6i) (which again may be actuated by movement of the cassette as previously mentioned) into its other position completes a circuit to the primary winding 28 of low tension transformer I8 causing its secondary winding Il to energize the large focalspot cathode 8 raising it to an electron emitting temperature. At the same time, however, energization of secondary winding il also causes discharge of condenser 4G through the cathode 8 to suddenly raise the temperature of the latter in'the manner previously described. In the modication of Fig. 2 it will be noted, however, that the large focal-spot cathode 8 is not preheated (although it may be if desired), and the energization of the transformer i8 also controls the simultaneous discharge of condenser 4S.

The latter is accomplished in the following manner: The trigger tube 42 is included in the discharge circuit of condenser 40 along with the The 6. cathode 8, and the control electrode-cathode'is supplied with a biasing potential from the battery 43 through resistance 44, in the identical manner as described relative to Fig. 1. However.,

instead of the control electrode-cathode of tube 42 being connected to an insulating transformer 46 and a control arrangement as in Fig. 1, the control electrode-cathode in this latter modification is connected through resistances 62 and 6'3 to the secondary winding Il' oftransformer I8. Consequently, upon closure of switch 60 to the radiographic position, with attendant energization of the large focal-spot cathode 8, the Voltage of the secondary winding l1 is applied through the resistances 62 and 63 across the control electrode and cathode of the trigger tube 42.

This immediately changes the biasing potential of the control electrode as supplied by the battery 43 from more negative with respect to the cathode to a more positive biasing potential with respect to the cathode making the tube immediately conductive, thus causing the condenser 4l) to discharge through the large focal-spot cathode 8, as mentioned above. The modication of Fig. 2 thus dispenses not only with the necessity for an insulation transformer, such as 46, but also eliminates the remainder of-the control arrangement of Fig. 1, including the additional control tube 5S and condenser 49, together with the various sources of supply, as well as a multi-contact relay 36 as shown in Fig. 1.

lt thus becomes obvious to those skilled in the art that an X-ray apparatus is herein provided for double-focus X-ray tubes wherein the apparatus is rapidly converted from its setting for fiuoroscopic purposes to a radiographic setting. Moreover, the change-over from the small focalspot cathode to the large focal-spot cathode is accompanied by substantially no time lag in the large focal-spot cathode reaching an electron emitting temperature. This is effected by discharging an energy storage means such as a condenser through the filamentary cathode which raises the latter to an electron emitting temperature in 0.1 of a second or less depending upon the voltage across the condenser.

Although two embodiments of the present invention have been shown and described, it isfto be understood that still further modications thereof may be made without departing from the spirit and scope of the appended claims.

I claim:

1. An X-ray apparatus for the making of fluoroscopic and radiographic examinations comprising an Y-ray tube provided with a small focal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means'for heating said small focal-spot producing `cathode to an electron emitting temperature for uoroscopic purposes, means operable to cause substantially instantaneous heating of said large focal-spot producing cathode to an electronemitting temperature for radiographic purposes, and means operable to interrupt the heating of said small focal-spot producing cathode and to cause the immediate operation of said last vmentioned means with attendant instantaneous heating of said large focal-spot producing cathodefrom' a source of supply independent of the means for heating the small focal-spot producing cathode.

2. An X-ray apparatus for the making of fluoroscopic and radiographic examinations coinprising an X-ray tube providedwith a smallifo- 7 cal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature for fluoroscopic purposes, means operable to cause the raising of said large focal-spot producing cathode to an electron emitting temperature in 0.1 of a second or less for radiographic purposes, and means operable' to interrupt the heating of said small focal-spot producing cathode and to cause the immediate operation of said last mentioned means with attendant instantaneous heating of said large focal-spot producing cathode from a source of supply independent of the means for heating the small focal-spot producing cathode.

3. An X-ray apparatus for the making of fluoroscopic and radiographic examinations comprising an X-ray tube provided with a small focal-spot producing cathode and a large focal-spot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature for iluoroscopic purposes, means operable to cause the momentary application of a source of energy to said large focal-spot producing cathode having a magnitude in excess of that required to maintain the latter at an electron emitting temperature to suddenly raise the large focal-spot producing cathode to an electron emitting temperature without an appreciable time lapse for purposes of radiography, and means operable to interrupt the heating of said small focal-spot producing cathode and to cause the immediate operation of said last mentioned means with attendant sudden heating of said large focal-spot producing cathode from a source of supply independent of the means for heating the small focal-spot producing cathode.

4. An X-ray apparatus for the making of fluoroscopic and radiographic examinations comprising an X-ray tube provided with a small focal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature for fluoroscopic purposes, energy storage means having a magnitude of electrical energy in excess of that required to maintain said large focal-spot producing cathode at an electron emitting temperature, and means operable to interrupt the heating of said small focal-spot producing cathode and to simultaneously cause the momentary discharge of said energy storage means directly through said large focal-spot producing cathode to suddenly raise the latter to an electron emitting temperature for purpose of radiography.

5. An X-ray apparatus for the making f iluoroscopic and radiographic examinations comprising an X-ray tube provided With a small focal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature for fluoroscopic purposes, means for heating said large focal-spot producing cathode to a temperature where no appreciable electron emission occurs, means operable to apply an energy impulse directly to said large focal-spot producing cathode of a magnitude in excess of that available from said last mentioned means to suddenly raise the large focal-spot producing cathode to an electron emitting temperature Without an appreciable time lapse for purposes of radiography, and means operable to interupt heating of said small focal-spot producing cathode and to cause the simultaneous operation of said last mentioned means with attendant application of an energy impulse to said large focal-spot producing cathode from a source of supply independent of the means for heating the small focal-spot producing cathode.

6. An X-ray apparatus for the making of fluoroscopic and radiographic examinations comprising an X-ray tube provided with a small focal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature for fluoroscopic purposes, means independent of said means for heating said small focal-spot producing cathode for normally heating said large focal-spot producing cathode to a temperature Where no appreciable electron emission occurs but adapted to raise and maintain the same at an electron emitting temperature, energy storage means of a magnitude greater than said last mentioned means and adapted to directly discharge its accumulated energy through said large focalspot producing cathode, and means operable to interrupt the heating of said small focal-spot producing cathode and to simultaneously cause said last mentioned means to heat said large focal-spot producing cathode to an electron emitting temperature together with momentary disl charge of said energy storage means through the latter to suddenly raise the large focal-spot producing cathode to an electron emitting temperature without an appreciable time lapse for purposes of radiography.

7. An X-ray apparatus for the making of iiuoroscopic and radiographic examinations comprising an X-ray tube provided with a small focal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature for fluoroscopic purposes, a low potential transformer independent of said means for heating said small focal-spot producing cathode for heating said large focal-spot producing cathode, an impedance device for normally limiting the energy supplied by said transformer to said large focal-spot producing cathode to maintain the latter at a temperature where no appreciable electron emission occurs, energy storage means having a magnitude of energy greater than that of said transformer and adapted to momentarily discharge its accumulated energy directly through said large focal-spot producing cathode, and means operable to interrupt the heating of said small focal-spot producing cathode and to simultaneously cause the short-circuiting of said variable impedance and discharge of said energy storage means to suddenly raise the large focal-spot producing cathode to an electron emitting temperature Without an appreciable time lapse for purposes of radiography.

8. An X-ray apparatus for the making of uoroscopic and radiographic examinations comprising an X-ray tube provided with a small Iocal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature for fluoroscopic purposes, energy storage means having .a magnitude of electrical energy in excess of that required to maintain said large focal-spot producing cathode at an electron emitting temperature, and a switch operable to cause interruption of the heating of said small focal-spot producing cathode and to cause the momentary discharge of said energy storage means directly through said large focal-spot producing cathode to. suddenly raise the latter to an electron emitting temperature for purposes of radiography.

9. An X-ray apparatus for the making of fluoroscopic and radiographic examinations comprising an X-ray tube provided with a small focal-spot producing cathode and a large focalspot producing cathode, a source of electrical energy for energizing said X-ray tube, means for heating said small focal-spot producing cathode to an electron emitting temperature :for` luoroscopic purposes, a low potential transformer independent of said means for heating said small focal-spot producing cathode for heating said large focal-spot producing cathode, an impedance device for normally limiting the energy supplied by said transformer to said large focal-spot producing cathode to maintain the latter at a temperature where no appreciable electron emission occurs, energy storage means having a magnitude of energy greater than that of said transformer, a control tube normally operable to prevent discharge of said energy storage means, and a switch operable to cause interruption of the heating of said small focal-spot producing cathode and short-circuiting of said impedance and to cause said control tube to become conductive with attendant momentary discharge of said energy storage means directly through said large focalspot producing cathode to suddenly raise the latter to an electron emitting temperature for purposes of radiography.

CHARLES M. SLACK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Eaton Apr. 29, 1941